excalidraw/src/clipboard.ts

import {
  ExcalidrawElement,
  NonDeletedExcalidrawElement,
} from "./element/types";
import { getSelectedElements } from "./scene";
import { AppState } from "./types";
import { SVG_EXPORT_TAG } from "./scene/export";
import { tryParseSpreadsheet, Spreadsheet, VALID_SPREADSHEET } from "./charts";
import { canvasToBlob } from "./data/blob";

const TYPE_ELEMENTS = "excalidraw/elements";

type ElementsClipboard = {
  type: typeof TYPE_ELEMENTS;
  created: number;
  elements: ExcalidrawElement[];
};

let CLIPBOARD = "";
let PREFER_APP_CLIPBOARD = false;

export const probablySupportsClipboardReadText =
  "clipboard" in navigator && "readText" in navigator.clipboard;

export const probablySupportsClipboardWriteText =
  "clipboard" in navigator && "writeText" in navigator.clipboard;

export const probablySupportsClipboardBlob =
  "clipboard" in navigator &&
  "write" in navigator.clipboard &&
  "ClipboardItem" in window &&
  "toBlob" in HTMLCanvasElement.prototype;

const isElementsClipboard = (contents: any): contents is ElementsClipboard => {
  if (contents?.type === TYPE_ELEMENTS) {
    return true;
  }
  return false;
};

export const copyToClipboard = async (
  elements: readonly NonDeletedExcalidrawElement[],
  appState: AppState,
) => {
  const contents: ElementsClipboard = {
    type: TYPE_ELEMENTS,
    created: Date.now(),
    elements: getSelectedElements(elements, appState),
  };
  const json = JSON.stringify(contents);
  CLIPBOARD = json;
  try {
    PREFER_APP_CLIPBOARD = false;
    await copyTextToSystemClipboard(json);
  } catch (error) {
    PREFER_APP_CLIPBOARD = true;
    console.error(error);
  }
};

const getAppClipboard = (): Partial<ElementsClipboard> => {
  if (!CLIPBOARD) {
    return {};
  }

  try {
    return JSON.parse(CLIPBOARD);
  } catch (error) {
    console.error(error);
    return {};
  }
};

const parsePotentialSpreadsheet = (
  text: string,
): { spreadsheet: Spreadsheet } | { errorMessage: string } | null => {
  const result = tryParseSpreadsheet(text);
  if (result.type === VALID_SPREADSHEET) {
    return { spreadsheet: result.spreadsheet };
  }
  return null;
};

/**
 * Retrieves content from system clipboard (either from ClipboardEvent or
 *  via async clipboard API if supported)
 */
const getSystemClipboard = async (
  event: ClipboardEvent | null,
): Promise<string> => {
  try {
    const text = event
      ? event.clipboardData?.getData("text/plain").trim()
      : probablySupportsClipboardReadText &&
        (await navigator.clipboard.readText());

    return text || "";
  } catch {
    return "";
  }
};

/**
 * Attemps to parse clipboard. Prefers system clipboard.
 */
export const parseClipboard = async (
  event: ClipboardEvent | null,
): Promise<{
  spreadsheet?: Spreadsheet;
  elements?: readonly ExcalidrawElement[];
  text?: string;
  errorMessage?: string;
}> => {
  const systemClipboard = await getSystemClipboard(event);

  // if system clipboard empty, couldn't be resolved, or contains previously
  // copied excalidraw scene as SVG, fall back to previously copied excalidraw
  // elements
  if (!systemClipboard || systemClipboard.includes(SVG_EXPORT_TAG)) {
    return getAppClipboard();
  }

  // if system clipboard contains spreadsheet, use it even though it's
  // technically possible it's staler than in-app clipboard
  const spreadsheetResult = parsePotentialSpreadsheet(systemClipboard);
  if (spreadsheetResult) {
    return spreadsheetResult;
  }

  const appClipboardData = getAppClipboard();

  try {
    const systemClipboardData = JSON.parse(systemClipboard);
    // system clipboard elements are newer than in-app clipboard
    if (
      isElementsClipboard(systemClipboardData) &&
      (!appClipboardData?.created ||
        appClipboardData.created < systemClipboardData.created)
    ) {
      return { elements: systemClipboardData.elements };
    }
    // in-app clipboard is newer than system clipboard
    return appClipboardData;
  } catch {
    // system clipboard doesn't contain excalidraw elements → return plaintext
    // unless we set a flag to prefer in-app clipboard because browser didn't
    // support storing to system clipboard on copy
    return PREFER_APP_CLIPBOARD && appClipboardData.elements
      ? appClipboardData
      : { text: systemClipboard };
  }
};

export const copyCanvasToClipboardAsPng = async (canvas: HTMLCanvasElement) => {
  const blob = await canvasToBlob(canvas);
  await navigator.clipboard.write([
    new window.ClipboardItem({ "image/png": blob }),
  ]);
};

export const copyTextToSystemClipboard = async (text: string | null) => {
  let copied = false;
  if (probablySupportsClipboardWriteText) {
    try {
      // NOTE: doesn't work on FF on non-HTTPS domains, or when document
      // not focused
      await navigator.clipboard.writeText(text || "");
      copied = true;
    } catch (error) {
      console.error(error);
    }
  }

  // Note that execCommand doesn't allow copying empty strings, so if we're
  // clearing clipboard using this API, we must copy at least an empty char
  if (!copied && !copyTextViaExecCommand(text || " ")) {
    throw new Error("couldn't copy");
  }
};

// adapted from https://github.com/zenorocha/clipboard.js/blob/ce79f170aa655c408b6aab33c9472e8e4fa52e19/src/clipboard-action.js#L48
const copyTextViaExecCommand = (text: string) => {
  const isRTL = document.documentElement.getAttribute("dir") === "rtl";

  const textarea = document.createElement("textarea");

  textarea.style.border = "0";
  textarea.style.padding = "0";
  textarea.style.margin = "0";
  textarea.style.position = "absolute";
  textarea.style[isRTL ? "right" : "left"] = "-9999px";
  const yPosition = window.pageYOffset || document.documentElement.scrollTop;
  textarea.style.top = `${yPosition}px`;
  // Prevent zooming on iOS
  textarea.style.fontSize = "12pt";

  textarea.setAttribute("readonly", "");
  textarea.value = text;

  document.body.appendChild(textarea);

  let success = false;

  try {
    textarea.select();
    textarea.setSelectionRange(0, textarea.value.length);

    success = document.execCommand("copy");
  } catch (error) {
    console.error(error);
  }

  textarea.remove();

  return success;
};